Under new rules posted by the Civil Aviation Administration of China on Friday, pilots will have to pass a “level four” test of Mandarin Chinese, China’s official language. Those who speak with an accent that “often impedes” comprehension will not pass. These rules take effect in January 2016.

China’s 56 ethnic groups speak more than 80 languages and dialects. Even native Mandarin speakers can have trouble communicating with each other depending on the the strength of their accents, which can be mutually unintelligible.

One flight trainer illustrated the scope for linguistic confusion, especially when common English aviation terms enter the equation. Asked if there is a problem on board, a Chinese pilot might answer in the negative with the words mei you, or “there isn’t”. But someone speaking with a heavy Sichuan accent would pronounce mei you as “may day” – unwittingly parroting the universally recognised distress call.